1. Field of the Invention
The present invention relates to a motor-driven pump applicable as a booster of combustible fluid such as liquid fuel in a rocket, and low-temperature or very-low-temperature fluid such as liquid oxygen or liquid helium.
2. Description of the Prior Art
One example of a heretofore known motor-driven pump is shown in FIG. 9. The heretofore known pump is operated with its rotary shaft 03 directly connected to a power source such as an electric motor or a turbine to be driven. In order to prevent fluid from flowing from the inside of the pump to the outside thereof or into an electric motor, the shaft is sealed by a packing 04. Reference numeral 05 designates a rotor of the electric motor, numeral 06 designates a stator, numeral 07 designates a bearing, and numeral 08 designates a packing gland.
As described above, the shaft of the pump in the prior art is sealed by packing 04 so that fluid will not flow from the inside of the pump to the outside or into an electric motor. Therefore, power loss and abrasion are caused by relative sliding movement between the rotary shaft 03 and the packing 04. Also, it is difficult to perfectly prevent fluid from leaking from the pump, and hence, combustible fluid could ignite or low-temperature and very-low-temperature fluid could freeze if leaked from the pump.